Uhmwpe fiber

ABSTRACT

The invention relates to a creep optimized gel-spun fiber comprising a polyethylene fiber body obtained by spinning an UHMWPE comprising alkyl branches (AB) and having an elongational stress (ES), and a ratio (I) of at least 0.2, wherein a stabilizer is present inside the fiber body, characterized in that the amount of said stabilizer is between 0.05 and 10 parts by weight based on 100 parts by weight of the amount of the PE forming said fiber body. 
     
       
         
           
             
               
                 
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This invention relates to a creep-optimized gel-spun fiber comprising apolyethylene fiber body obtained, a process for producing the same andvarious products such as ropes, nets, medical devices, fabrics,laminates, composite articles and ballistic-resistant articlescontaining said fibres.

During the last decades, many research projects focused on improving thecreep properties of synthetic fibers, since such fibers are extremelysuitable for a wide range of applications where lightweight and strengthare driving factors. One example of synthetic fibers is UHMWPE fibers,which meet successfully the weight and strength requirements. The almostunmatched strength of UHMWPE fibers combined with ultravioletresistance, chemical resistance, cut and abrasion resistance and otherfavorable properties are the reasons that these fibers found an almostimmediate utilization in rope mooring, composite reinforcement, medicaldevices, cargo nets and the like.

UHMWPE fibers have however one drawback which acts as an impediment fortheir optimal utilization in long-term applications, this drawback beingrelated to their creep behavior. It was observed that the ultimatefailure mode of a system using UHMWPE fibers and in particular of thosesystems placed under a long-term load, is rupture or failure due tocreep. Such systems and particularly those intended for long-term orultralong-term use must therefore be over-designed to last for a largenumber of years, e.g. more than 10 years and in some cases more thaneven 30 years. Therefore, an immediate need was felt in the industry,i.e. the need for an UHMWPE fiber having an optimized creep behavior.Accordingly many research projects aiming to improving UHMWPE fibersfocused on their creep behavior and almost all these projects focusedsolely on optimizing a creep rate thereof.

For example, WO 2009/043598 and WO 2009/043597 disclose UHMWPE fibershaving a good combination of creep rate and tensile strength, e.g. acreep rate of at most 5×10⁻⁷ sec⁻¹ as measured at 70° C. under a load of600 MPa, and a tensile strength of at least 4 GPa.

More recently example for fibers with good creep behaviour and a processfor producing thereof are known from WO2012139934; disclosing UHMWPEfibres having creep lifetime as high as 500 hours as measured at 70° C.under a load of 600 MPa and tensile strengths as high as 4.1 GPa.

Although the fibers known from the prior art have acceptable creeplifetime and/or creep rate, there remains a need to further optimize thelong term creep properties, also called survivability.

An aim of the present invention may therefore be to provide an UHMWPEfiber having an optimized survivability. A further aim of the presentinvention may be to provide an UHMWPE fiber having an optimizedsurvivability and also good tensile properties, e.g. tensile strength,tensile modulus and/or elongation at break. A yet further aim of thepresent invention may be to provide an UHMWPE fiber having an improvedsurvivability when compared to the survivability of the existing UHMWPEfibers.

The invention provides a creep optimized gel-spun fiber comprising apolyethylene fiber body obtained by spinning an UHMWPE comprising alkylbranches (AB) and having an elongational stress (ES), and a ratio

$\left( \frac{A\; {B/1000}\; C}{E\; S} \right)$

between the number of alkyl branches per thousand carbon atoms(AB/1000C) and the elongational stress (ES) of at least 0.2, wherein astabilizer is present inside the fiber body, characterized in that theamount of said stabilizer is between 0.05 and 10 parts by weight basedon 100 parts by weight of the amount of the UHMWPE forming said fiberbody.

It was observed that by optimizing the creep lifetime of a fiber, itssurvivability under a long-term load may also be optimized. Inparticular it was observed that inventive UHMWPE fibers may be producedin accordance with the invention, said fibers having a creep lifetimenever achieved hitherto by any existing UHMWPE fiber. It was alsoobserved that due to its optimized creep properties the inventive UHMWPEfiber is useful in a variety of applications and in particular in thoseapplications where a long- or an ultralong-term load is applied on saidfibers, e.g. offshore oil production platform mooring. By ultralong-termload is herein understood a load that is applied on the inventive UHMWPEfibers for at least 5 years, more preferably at least 10 years, morepreferably for at least 20 years, preferably under normal use conditionse.g. of humidity, temperature and load. For example, for offshoremooring, normal load conditions may be loads of at most 70% of thebreaking load of the fibers or of the product containing said fiberssuch as ropes; and normal temperature conditions may be the temperatureof the environment, e.g. of water at various depths or above water. Theinventors also observed that the design of systems or devices intendedfor long-term and ultralong-term applications and comprising theinventive UHMWPE fibers, may be less complicated and laborious.

It has also been surprisingly discovered that incorporation ofstabilizers and in particular UV stabilizers in the fiber body furtheroptimizes the creep lifetime of the UHMWPE fibers. Moreover, saidstabilizers optimally protect the fiber against degradation, whilehaving an acceptable influence on the mechanical properties, e.g.tensile strength, thereof.

According to the invention, a stabilizer is present inside the fiberbody. By stabilizer is herein understood a compound which contributes tothe stabilization of one or more fiber properties, e.g. mechanicalproperties such as tensile strength, elongation at break and modulus butalso other chemical or physical properties such as bio-degradability, UVresistance, thermo-oxidative stability and the like. By stabilization ofa fiber property is herein meant that said compound contributes inmaintaining that property within acceptable limits during a set periodof time.

By fibre is herein understood an elongated body, e.g. a body having alength and transverse dimensions, wherein the length of the body is muchgreater than its transverse dimensions. The term fibre as used hereinmay also include various embodiments, e.g. a filament, a tape, a strip,a ribbon and a yarn. The fiber may also have regular or irregularcross-sections. The fiber may also have a continuous and/or adiscontinuous length. Preferably, the fiber has a continuous length,such fiber being known in the art as a filament. Within the context ofthe invention, a yarn is understood to be an elongated body comprising aplurality of fibres.

Preferably, the stabilizer is present in an amount of at least 0.05,more preferably at least 0.075, even more preferably at least 0.1 partsby weight based on 100 parts by weight of the amount of the polyolefinpolymer forming the fiber body. Preferably, said stabilizer's amount isat most 10, more preferably at most 8, even more preferably at most 6,yet even more preferably at most 5, most preferably at most 3 parts byweight based on 100 parts by weight of the amount of the polyethylenepolymer forming the fiber body. In a preferred embodiment, the amount ofstabilizers is between 0.05 and 5 parts by weight, more preferably 0.05and 1 parts by weight based on 100 parts by weight of the amount of thepolyethylene polymer forming the fiber body.

Preferred stabilizers suitable for the invention are hindered aminestabilizers (HAS). Although, HAS are known as stabilizers forpolyethylene, it was hitherto impossible to incorporate them in asufficient amount in fibers such that these stabilizers wouldeffectively protect said fibers.

It was also surprisingly observed that HAS interfered to a lesser extentthan other stabilizers with the gel-spinning process of making agel-spun UHMWPE fiber. While when using various stabilizers in saidprocess, the spinning parameters, e.g. spinning tension, drawingpatterns, polymer concentration and type, etc., needed to be re-adjustedto accommodate for the addition of said stabilizers, it was observedthat when using HAS, essentially the same spinning parameters as for aconventional gel-spinning process, i.e. without stabilizers, could havebeen used. In other words, essentially no re-adjustment of the spinningparameters is needed when using HAS.

The invention also relates to a gel-spun fiber comprising a PE polymerforming a fiber body, wherein a HAS is present inside the fiber body,wherein the amount of HAS is preferably at least 0.05 parts by weightbased on 100 parts by weight of the amount of the PE polymer formingsaid fiber body. Preferably, the amount of HAS is at most 1.0 parts byweight based on 100 parts by weight of the amount of the polyolefinpolymer forming said fiber body. The invention further relates to a yarncontaining said fibers, the yarn having a titer of between 5 dtex and400 dtex, more preferably between 10 dtex and 250 dtex, most preferablybetween 20 dtex and 150 dtex.

Preferred HAS compounds include those of the following general formulasor combinations thereof;

wherein R₁ up to and including R₅ are independent substituents; forexample containing hydrogen, ether, ester, amine, amide, alkyl, alkenyl,alkynyl, aralkyl, cycloalkyl and/or aryl groups, which substituents mayin turn contain functional groups, for example alcohols, ketones,anhydrides, imines, siloxanes, ethers, carboxyl groups, aldehydes,esters, amides, imides, amines, nitriles, ethers, urethanes and anycombination thereof.

Preferably the HAS is a compound derived from a substituted piperidinecompound, in particular any compound which is derived from analkyl-substituted piperidyl, piperidinyl or piperazinone compound or asubstituted alkoxypiperidinyl. Other suitable HAS are those that arederivatives of 2,2,6,6-tetramethyl piperidine.

Preferred specific examples of HAS include:

-   (1) Bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate-   (2) Bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate-   (3)    Tetrakis(2,2,6,6-tetramethyl-4-piperidyl)-1,2,3,4-butanetetracaboxylate-   (4) 2,2,6,6-Tetramethyl-4-piperidyl benzoate-   (5)    Bis(1,2,2,6,6-pentamethyl-4-piperidyl)-2-(3,5-t-butyl-4-hydroxybenzyl)-2-n-butylmalonate-   (6) 1,1-(1,2-Ethanediyl)bis(3,3,5,5-tetramethyl)piperazinone-   (7)    (2,2,6,6-Tetramethyl-4-piperidyl/tridecyl)-1,2,3,4-butanetetracarboxylate-   (8)    (1,2,2,6,6-Pentamethyl-4-piperidyl/tridecyl)-1,2,3,4-butanetetracaboxylate-   (9)    {2,2,6,6-Tetramethyl-4-piperidyl/β,β,β′,β′-tetramethyl-3,9-[2,4,8,10-tetraoxasprio(5,5)-undecane]diethyl}-1,2,3,4-butanetetracarboxylate-   (10)    {1,2,2,6,6-Pentamethyl-4-piperidyl/β,β,β′,β′-tetramethyl-3,9-[2,4,8,10-tetraoxasprio(5,5)-undecane]diethyl}-1,2,3,4-butanetetracarboxylate-   (11)    N,N′-Bis(3-aminopropyl)ethylenediamine-2,4-bis-[N-butyl-N-(1,2,2,6,6-pentamethyl-4-piperidyl)amino]-6-chloro-1,3,5-triazine    condensate-   (12)    [N-(2,2,6,6-tetramethyl-4-piperidyl)-2-methyl-2-(2,2,6,6-tetramethyl-4-piperidyl)imino]propionamide.

More preferred HAS are:

wherein n is preferably from 1 to 50. Such compound may be obtained bythe reaction of dimethyl succinate with4-hydroxy-2,2,6,6-tetramethyl-1-piperidine ethanol. Such compound isknown as Dimethyl succinate polymer with4-hydroxy-2,2,6,6-tetramethyl-1-piperidine ethanol;

wherein n is preferably from 1 to 50. Such compound is known asPoly{[[6-[(1,1,3,3-tetramethylbutyl)amino]-s-triazine-2,4-diyl][(2,2,6,6-tetramethyl-4-piperidinyl)imino]hexamethylene[(2,2,6,6-tetramethyl-4-piperidinyl)imino]]};

wherein n is preferably from 1 to 50. Such compound is known asPoly[[(2,2,6,6-tetramethyl-4-piperidinyl)imino]-1,2-ethanediyl[(2,2,6,6-tetramethyl-4-piperidinyl)imino]-1,6-hexanediyl;

wherein n is preferably from 1 to 50. Such compound is known asPoly[(6-morpholino-s-triazine-2,4-diyl)[2,2,6,6-tetra-methyl-4-piperidyl)imino]-hexamethylene[(2,2,6,6-tetra-methyl-4-piperidyl)imino]];

wherein n is preferably from 1 to 50. Such compound is known as1,2,3,4-Butanetetracarboxylic acid, polymer withβ,β,β′,β′-tetramethyl-2,4,8,10-tetraoxaspiro[5.5]undecane-3,9-diethanol,1,2,2,6,6-pentamethyl-4-piperidinyl ester;

wherein n is preferably from 1 to 50. Such compound is known as1,2,3,4-Butanetetracarboxylic acid, polymer withβ,β,β′,β′-tetramethyl-2,4,8,10-tetraoxaspiro[5.5]undecane-3,9-diethanol,2,2,6,6-tetramethyl-4-piperidinyl ester;

Further suitable HAS compounds include:

such compound being known as 1,3,5-Triazine-2,4,6-triamine,N,N′″-[1,2-ethanediylbis[[[4,6-bis[butyl(1,2,2,6,6-pentamethyl-4-piperidinyl)amino]-1,3,5-triazine-2-yl]imino]-3,1-propanediyl]]-bis[N′,N″-dibutyl-N′,N″-bis(1,2,2,6,6-pentamethyl-4-piperidinyl).

and wherein n is preferably from 1 to 50. Such compound is known as1,3-Propanediamine, N,N-1,2-ethanediylbis-, polymer with2,4,6-trichloro-1,3,5-triazine, reaction products withN-butyl-2,2,6,6-tetramethyl-4-piperidinamine;

wherein n is preferably from 1 to 50. Such compound is known as2,2,4,4-Tetramethyl-7-oxa-20-(oxiranylmethyl)-3,20-diazadispiro(5.1.11.2)henicosan-21-one;

wherein n is preferably from 1 to 50. Such compound is known aspoly[oxy[methyl[3-[(2,2,6,6-tetramethyl-4-piperidinyl)oxy]propyl]silylene]]Poly-methylpropyl-3-oxy[4(2,2,6,6-tetramethyl)-piperidinyl]-siloxane;

wherein both m and n are preferably from 1 to 50. Such compound is acopolymer of α-methyl-styrene andN-(2,2,6,6-tetra-methyl-piperidinyl)-4-maleimide and n-stearylmaleimide.

wherein n is preferably from 1 to 50.

known as2,9,11,13,15,22,24,26,27,28-Decaazatricyclo[21.3.1.110,14]octacosa-1(27),10,12,14(28),23,25-hexaene-12,25-diamine,N,N′-bis(1,1,3,3-tetramethylbutyl)-2,9,15,22-tetrakis(2,2,6,6-tetramethyl-4-piperidinyl).

wherein n is preferably from 1 to 50. Such compound is known aspoly[(6-morpholino-s-triazine-2,4-diyl)[1,2,2,6,6-penta-methyl-4-piperidyl)imino]-hexamethylene[(1,2,2,6,6penta-methyl-4-piperidyl)imino]];

wherein n is preferably from 1 to 50. Such compound is known aspoly-methoxypopyl-3-oxy[4(1,2,2,6,6-pentamethyl)-piperidinyl]-siloxane.

wherein n is preferably from 1 to 50. Such compound is known as1,6-Hexanediamine, N,N′-bis(2,2,6,6-tetramethyl-4piperidinyl)-polymerwith 2,4,6-trichloro-1,3,5-triazine, reaction products withN-butyl-1-butanamine and N-butyl-2,2,6,6-tetramethyl-4-piperidinamine.

Such compounds may be reaction products ofN,N′-ethane-1,2-diylbis(1,3-propanediamine), cyclohexane, peroxidized4-butylamino-2,2,6,6-tetramethylpiperidine and2,4,6-trichloro-1,3,5-triazine;

wherein n is preferably from 1 to 50. Such compound is known as1,6-hexanediamine, N,N′-bis(2,2,6,6-tetramethyl-4-piperidinyl)-, polymerwith 2,4,6-trichloro-1,3,5-triazine, reaction products with3-bromo-1-propene, n-butyl-1-butanamine andN-butyl-2,2,6,6-tetramethyl-4-piperidinamine, oxidised, hydrogenated.

wherein R is a fatty acid.

Also preferred are HAS containing a group via which the HAS can begrafted to the PO. A suitable example thereof include 2-Butenedioic acid(E)-, bis(2,2,6,6-tetramethyl-4-piperidinyl) ester polymer with1-propene:

Preferably HAS have a molecular weight of at least 450 g/mol, morepreferably at least 1000 g/mol, more preferably at least 1250 g/mol,even more preferably at least 1500 g/mol.

Also the HAS known asPoly[[6-[(1,1,3,3-tetramethylbutyl)amino]-1,3,5-triazine-2,4-diyl][(2,2,6,6-tetramethyl-4-piperidinyl)imino]-1,6-hexanediyl[(2,2,6,6-tetramethyl-4-piperidinyl)imino]])and having the formula:

is preferred for utilization in accordance with the invention, the M_(n)thereof being preferably between 2000 and 3100.

When the fibers of the invention are gel-spun fibers, the HAS used inaccordance with the invention are preferably soluble in the solvent usedfor the UHMWPE, e.g. decalin. Preferably the HAS has a solubility of atleast 1 g/l of the solvent used in step a) at a temperature of 21° C.,more preferably the stabilizer has a solubility of at least 10 g/l.

All of the above mentioned HAS may be used either alone or in acombination with each other.

A further type of stabilizers suitable for the present invention includephenolic stabilizers, concrete examples thereof including thosementioned in EP 0 343 863 A2 from page 5, line 4 to page 6, line 25;included herein by reference. One group of phenolic stabilizers isnatural phenolic antioxidants including Vitamin E. Natural phenolicantioxidants and especially Vitamin E are highly preferred stabilizersparticularly for medical applications. The phenolic stabilizers may beused either alone or in combination of two or more.

A further type of stabilizers suitable for the present invention includeorganic phosphite stabilizers, concrete examples thereof including thosementioned in EP 0 343 863 A2 from page 6, line 43 to page 7, line 34;included herein by reference. These organic phosphite stabilizers may beused either alone or in combination of two or more.

A further type of stabilizers suitable for the present invention includeorganic thioether stabilizers, concrete examples thereof including thosementioned in EP 0 343 863 A2 at page 7 from line 53 to line 58; includedherein by reference. These organic thioether stabilizers may be usedeither alone or in combination of two or more.

Other suitable stabilizers for use in the present invention are thoseselected from the group consisting of hindered phenols, aromaticphosphites, amines and their mixture. Preferably, the stabilizer isselected from the group consisting of(2,6-di-tert-butyl-4-methyl-phenol,tetrakis[methylene(3,5-di-tert-butylhydroxyhydrocinnamate)]methane,tris(2,4-di-tert-butylphenyl)phosphite, octadecyl3,5-di-tert-butyl-4-hydroxyhydrocinnamate,1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione,2,5,7,8-tetramethyl-2(4′,8′,12′-trimethyltridecyl)chroman-6-ol and theirmixtures. More preferably the anti-oxidant is2,5,7,8-tetramethyl-2(4′,8′,12′-trimethyltridecyl)chroman-6-ol commonlyknown as Vitamin E or α-tocopherol.

Preferably, the alkyl branches of the UHMWPE have a number of carbonatoms between 1 and 15, more preferably between 2 and 10, mostpreferably between 2 and 6. Good results were obtained when the brancheswere ethyl branches (C=2) or butyl branches (C=4).

Therefore in one embodiment, the invention provides a creep-optimizedfiber obtained by spinning an UHMWPE comprising ethyl branches andhaving an intrinsic viscosity (IV) of at least 5 dl/g, an elongationalstress (ES), and a ratio

$\left( \frac{C\; 2H\; {5/1000}C}{E\; S} \right)$

between the number of ethyl branches per thousand carbon atoms(C2H5/1000C) and the elongational stress (ES) of at least 0.5,preferably at least 1.0. Preferably, the fiber of this embodiment whenpre-conditioned for 48 h at 100° C. and subjected to a load of 600 MPaat a temperature of 70° C., has a creep lifetime of at least 90 hours,preferably of at least 100 hours, more preferably of at least 110 hours,even more preferably of at least 120 hours, most preferably of at least125 hours.

In a preferred embodiment, the fiber is obtained by spinning an UHMWPEcomprising ethyl branches wherein the UHMWPE has an amount of ethylbranches per thousand carbon atoms (C2H5/1000C) of between 0.60 and1.10.

In another embodiment, the invention provides a creep-optimized UHMWPEfiber obtained by spinning an UHMWPE comprising butyl branches andhaving an intrinsic viscosity (IV) of preferably at least 5 dl/g, anelongational stress (ES), and a ratio

$\left( \frac{C\; 4H\; {9/1000}C}{E\; S} \right)$

between the number of butyl branches per thousand carbon atoms(C4H9/1000C) and the elongational stress (ES) of at least 0.2.Preferably, the fiber of this embodiment when pre-conditioned for 48 hat 100° C. and subjected to a load of 600 MPa at a temperature of 70°C., has a creep lifetime of at least 90 hours, preferably of at least100 hours, more preferably of at least 110 hours, even more preferablyof at least 120 hours, most preferably of at least 125 hours.

Preferably, the creep lifetime of the inventive UHMWPE fibers asdescribed in the embodiments hereinabove, is at least 150 hours, morepreferably at least 200 hours, even more preferably at least 250 hours,even more preferably at least 290 hours, yet even more preferably atleast 350 hours, yet even more preferably at least 400 hours, mostpreferably at least 445 hours. Such good creep lifetimes wereparticularly obtained for the embodiments of fibers spun from UHMWPEswherein the stabilizer was a hindered amine stabilizers (HAS) having amolecular weight of at least 500 g/mol. The creep lifetime is measuredon multifilament yarns in accordance with the methodology described inthe METHODS FOR MEASUREMENT section hereinbelow.

Preferably, the inventive UHMWPE fibers and in particular those spunfrom UHMWPEs having ethyl or butyl branches, have a tenacity of at least25 cN/dtex, more preferably of at least 32 cN/dtex, most preferably ofat least 38 cN/dtex. Preferably, the inventive UHMWPE fibers and inparticular those spun from UHMWPEs having ethyl or butyl branches, havean elastic modulus of at least 1100 cN/dtex, more preferably of at least1200 cN/dtex, most preferably of at least 1300 cN/dtex. It was observedthat in addition to the excellent creep properties, the inventive UHMWPEfibers have also good tensile properties.

According to the invention, the inventive UHMWPE fibers are obtained bya gel spinning process. Therefore, the fibers of the invention arepreferably obtained by gel-spinning an UHMWPE comprising ethyl branchesor butyl branches and having a number of branches per thousand carbonatoms, an ES and an IV as described throughout the present document.

For the present invention, by gel-spinning process is meant a processcomprising at least the steps of (a) preparing a solution comprising anUHMWPE and a suitable solvent for UHMWPE; (b) extruding said solutionthrough a spinneret to obtain a gel fiber containing said UHMWPE andsaid solvent for UHMWPE; and (c) extracting the solvent from the gelfiber to obtain a solid fiber. The gel-spinning process may alsooptionally contain a drawing step wherein the gel fiber and/or the solidfiber are drawn with a certain draw ratio. Gel spinning processes areknown in the art and are disclosed for example in WO 2005/066400; WO2005/066401; WO 2009/043598; WO 2009/043597; WO 2008/131925; WO2009/124762; EP 0205960 A, EP 0213208 A1, U.S. Pat. No. 4,413,110, EP0200547 B1, EP 0472114 B1, WO 2001/73173 A1 and EP 1,699,954, thesepublications and the references cited therein being included herein byreference.

According to the invention, the gel-spinning process for manufacturingthe inventive UHMWPE fibers, uses an UHMWPE polymer. By UHMWPE is hereinunderstood a polyethylene having an intrinsic viscosity (IV) as measuredon solution in decalin at 135° C., of preferably at least 5 dl/g.Preferably, the IV of the UHMWPE is at least 10 dl/g, more preferably atleast 15 dl/g, even more preferably at least 19 dl/g, most preferably atleast 21 dl/g. Preferably, the IV is at most 40 dl/g, more preferably atmost 30 dl/g, even more preferably at most 25 dl/g.

The UHMWPE used in the present invention has preferably a ratio

$\frac{A\; {B/1000}\; C}{E\; S}$

of at least 0.3, more preferably of at least 0.4, even more preferablyof at least 0.5, yet even more preferably of at least 0.7, yet even morepreferably of at least 1.0, yet even more preferably of at least 1.2. Itwas surprisingly observed that by increasing the above mentioned ratio,the properties of the inventive UHMWPE fibers may be improved.

When the UHMWPE used in the present invention has ethyl branches, saidUHMWPE preferably has a ratio

$\left( \frac{C\; 2H\; {5/1000}C}{E\; S} \right)$

of at least 1.00, more preferably of at least 1.30, even more preferablyof at least 1.45, yet even more preferably of at least 1.50, mostpreferably of at least 2.00. Preferably said ratio is between 1.00 and3.00, more preferably between 1.20 and 2.80, even more preferablybetween 1.40 and 1.60, yet even more preferably between 1.45 and 2.20.

When the UHMWPE used in the present invention has butyl branches, saidUHMWPE preferably has a ratio

$\left( \frac{C\; 4H\; {9/1000}C}{E\; S} \right)$

of at least 0.25, even more preferably at least 0.30, yet even morepreferably at least 0.40, yet even more preferably at least 0.70, morepreferably of at least 1.00, most preferably of at least 1.20.Preferably said ratio is between 0.20 and 3.00, more preferably between0.40 and 2.00, even more preferably between 1.40 and 1.80.

The UHMWPE used in the present invention has preferably an ES of at most0.70, more preferably of at most 0.50, more preferably of at most 0.49,even more preferably at most 0.45, most preferably at most 0.40. Whensaid UHMWPE has ethyl branches, preferably said UHMWPE has an ES ofbetween 0.30 and 0.70, more preferably between 0.35 and 0.50. When saidUHMWPE has butyl branches, preferably said UHMWPE has an ES of between0.30 and 0.50, more preferably between 0.40 and 0.45.

The UHMWPE used according to the invention, also has preferably anamount of alkyl branches per thousand carbon atoms (AB/1000C) of between0.05 and 1.30, more preferably between 0.10 and 1.10, even morepreferably between 0.30 and 1.05.

When the UHMWPE used according to the invention has ethyl branches,preferably said UHMWPE has an amount of ethyl branches per thousandcarbon atoms (C2H5/1000C) of between 0.40 and 1.10, more preferablybetween 0.60 and 1.10. In a first preferred embodiment, the C2H5/1000Cis between 0.63 and 0.75, preferably between 0.64 and 0.72, morepreferably between 0.65 and 0.70. For the first preferred embodiment, itwas observed that the tensile properties of the inventive UHMWPE fiberswere improved while also achieving a unique creep lifetime. In a secondpreferred embodiment, the C2H5/1000C is between 0.78 and 1.10,preferably between 0.90 and 1.08, more preferably between 1.02 and 1.07.For the second preferred embodiment it was observed that the creeplifetime of the inventive UHMWPE fibers was improved.

When the UHMWPE used according to the invention has butyl branches,preferably said UHMWPE has an amount of butyl branches per thousandcarbon atoms (C4H9/1000C) of between 0.05 and 0.80, more preferablybetween 0.10 and 0.60, even more preferably between 0.15 and 0.55, mostpreferably between 0.30 and 0.55.

Preferably, any ones of the UHMWPEs used according to the invention areobtained by a slurry polymerisation process in the presence of an olefinpolymerisation catalyst at a polymerisation temperature. The process forthe manufacturing of the used UHMWPE is described in detail inWO2012139934, which is herewith included by reference,

According to the invention, a gel-spinning process is used tomanufacture the inventive UHMWPE fibers, wherein as already mentionedhereinabove, the UHMWPE is used to produce an UHMWPE solution, which issubsequently spun through a spinneret and the obtained gel fiber isdried to form a solid fiber.

The UHMWPE solution is preferably prepared with a UHMWPE concentrationof at least 3 mass-%, more preferably of at least 5 mass-%. Preferably,the concentration is between 3 and 15 mass-% for UHMWPE with IV in therange 15-25 dl/g.

To prepare the UHMWPE solution, any of the known solvents suitable forgel spinning the UHMWPE may be used. Such solvents are also referred toherein as “spinning solvents”. Suitable examples of solvents includealiphatic and alicyclic hydrocarbons, e.g. octane, nonane, decane andparaffins, including isomers thereof; petroleum fractions; mineral oil;kerosene; aromatic hydrocarbons, e.g. toluene, xylene, and naphthalene,including hydrogenated derivatives thereof, e.g. decalin and tetralin;halogenated hydrocarbons, e.g. monochlorobenzene; and cycloalkanes orcycloalkenes, e.g. careen, fluorine, camphene, menthane, dipentene,naphthalene, acenaphtalene, methylcyclopentandien, tricyclodecane,1,2,4,5-tetramethyl-1,4-cyclohexadiene, fluorenone, naphtindane,tetramethyl-p-benzodiquinone, ethylfuorene, fluoranthene andnaphthenone. Also combinations of the above-enumerated solvents may beused for gel spinning of UHMWPE, the combination of solvents being alsoreferred to for simplicity as solvent. In a preferred embodiment, thesolvent of choice is not volatile at room temperature, e.g. paraffinoil. It was also found that the process of the invention is especiallyadvantageous for relatively volatile solvents at room temperature, asfor example decalin, tetralin and kerosene grades. In the most preferredembodiment the solvent of choice is decalin.

The UHMWPE solution is then formed into gel filaments by spinning saidsolution through a spinneret preferably containing multiple spinholes.By spinneret containing multiple spinholes is herein understood aspinneret containing preferably at least 100, yet even more preferablyat least 300, most preferably at least 500 spinholes. Preferably, thespinning temperature is between 150° C. and 250° C., more preferablysaid temperature is chosen below the boiling point of the spinningsolvent. If for example decaline is used as spinning solvent thespinning temperature is preferably at most 190° C.

The gel filaments formed by spinning the UHMWPE solution through thespinneret are extruded into an air gap, and then into a cooling zonefrom where they are picked-up on a first driven roller. Preferably, thegel filaments are stretched in the air gap. In the cooling zone, the gelfilaments are cooled preferably in a gas flow and/or in a liquid bath.

Subsequently to forming the gel filaments, said gel filaments aresubjected to a solvent extraction step wherein the spinning solvent usedto manufacture the UHMWPE solution is at least partly removed from thegel filaments to form solid filaments. The solvent removal process maybe performed by known methods, for example by evaporation when arelatively volatile spinning solvent, e.g. decaline, is used or by usingan extraction liquid, e.g. when paraffin is used as spinning solvent, orby a combination of both methods. Preferably the gel filaments are drawnwith a draw ratio of preferably at least 1.2, more preferably at least1.5, most preferable at least 2.0.

Preferably, the solid filaments are also drawn during and/or after saidremoval of the solvent. Preferably, the drawing of the solid filamentsis performed in at least one drawing step with a draw ratio ofpreferably at least 4, more preferably at least 7, even more preferablyat least 10. More preferably, the drawing of solid filaments isperformed in at least two steps, even more preferably in at least threesteps.

The inventive UHMWPE fibres have properties which make them aninteresting material for use in ropes, cordages and the like, preferablyropes designed for heavy-duty operations as for example marine,industrial and offshore operations. Rigging ropes and ropes used insports applications such as yachting, climbing, kiteflying, parachutingand the like are also applications where the fibers of the invention mayperform well. In particular it was observed that the inventive UHMWPEfibers are particularly useful for long-term and ultralong-termheavy-duty operations.

Heavy duty operations may further include, but not restricted to, craneropes, ropes for deep-sea deployment or recovery of hardware, anchorhandling, mooring of support platforms for offshore renewable energygeneration, mooring of offshore oil drilling rigs and productionplatforms such as offshore production platforms and the like. It wassurprisingly observed that for such operations, and in particular foroffshore mooring, the installation of ropes designed therefor may beoptimized, e.g. the ropes can be installed using less complex hardwareor smaller and lighter installation equipment.

The inventive UHMWPE fibers are also very suitable for use as areinforcing element, for example in a liner, for reinforced productssuch as hoses, pipes, pressurized vessels, electrical and opticalcables, especially when said reinforced products are used in deepwaterenvironments where reinforcement is required to support the load of thereinforced products when free hanging. The invention therefore alsorelates to a liner and a reinforced product containing reinforcingelements or containing said liner, wherein the reinforcing elements orthe liner contain the inventive UHMWPE fibers.

Most preferably, the inventive UHMWPE fibres are used in applicationswhere said fibres experience static tension or static loads and inparticular long-term and ultralong-term static tension or static loads.By static tension is herein meant that the fibre in application alwaysor most of the time is under tension irrespective if the tension is atconstant level (for example a weight hanging freely in a rope comprisingthe fibre) or varying level (for example if exposed to thermal expansionor water wave motion). Examples of applications wherein static tensionsare encountered are for example many medical applications (for examplecables and sutures) but also mooring ropes, and tension reinforcementelements, as the improved creep lifetime of the present fibres leads toimproved performances of these and similar applications. A particularapplication of the inventive UHMWPE fibers is in crane ropes where therope can reach an elevated temperature as result of (1) ambienttemperatures and/or (2) internal heat generation due to friction aroundcrane sheaves.

Therefore, the invention relates to ropes and in particular mooringropes, with or without a cover, containing the inventive UHMWPE fibres.Preferably, at least 50 mass-%, more preferably at least 75 mass-%, evenmore preferably at least 90 mass-% from the total mass of the fibresused to manufacture the rope and/or the cover consists of the inventiveUHMWPE fibres. Most preferably the mass of fibers used to manufacturethe rope and/or the cover consists of the inventive UHMWPE fibres. Theremaining mass percentage of the fibres in the rope according to theinvention, may contain fibres or combination of fibers made of othermaterials suitable for making fibres as for example metal, glass,carbon, nylon, polyester, aramid, other types of polyolefin and thelike.

The invention further relates to composite articles containing theinventive UHMWPE fibres.

In a preferred embodiment, the composite article contains at least onemono-layer comprising the UHMWPE fibres of the invention. The termmono-layer refers to a layer of fibers, i.e. fibers in one plane. In afurther preferred embodiment, the mono-layer is a unidirectionalmono-layer. The term unidirectional mono-layer refers to a layer ofunidirectionally oriented fibers, i.e. fibers in one plane that areessentially oriented in parallel. In a yet further preferred embodiment,the composite article is multi-layered composite article, containing aplurality of unidirectional mono-layers the direction of the fibres ineach mono-layer preferably being rotated with a certain angle withrespect to the direction of the fibres in an adjacent mono-layer.Preferably, the angle is at least 30°, more preferably at least 45°,even more preferably at least 75°, most preferably the angle is about90°. Multi-layered composite articles proved very useful in ballisticapplications, e.g. body armor, helmets, hard and flexible shield panels,panels for vehicle armouring and the like. Therefore, the invention alsorelates to ballistic-resistant articles as the ones enumeratedhereinabove containing the UHMWPE fibres of the invention.

The inventive UHMWPE fibres of the invention are also suitable for usein medical devices, e.g. sutures, medical cables, implants, surgicalrepair products and the like. The invention therefore further relates toa medical device, in particular to a surgical repair product and more inparticular to a suture and to a medical cable comprising the UHMWPEfibres of the invention.

It was also observed that the inventive UHMWPE fibres are also suitablefor use in other applications like for example, synthetic chains,conveyor belts, tensiarity structures, concrete reinforcements, fishinglines and fishing nets, ground nets, cargo nets and curtains, kitelines, dental floss, tennis racquet strings, canvas (e.g. tent canvas),nonwoven cloths and other types of fabrics, webbings, batteryseparators, capacitors, pressure vessels (e.g. pressure cylinders,inflatables), hoses, (offshore) umbilical cables, electrical, opticalfiber, and signal cables, automotive equipment, power transmissionbelts, building construction materials, cut and stab resistant andincision resistant articles, protective gloves, composite sportsequipment such as skis, helmets, kayaks, canoes, bicycles and boat hullsand spars, speaker cones, high performance electrical insulation,radomes, sails, geo-textiles such as mats, bags and nets, and the like.Therefore, the invention also relates to the applications enumeratedabove containing the UHMWPE fibers of the invention.

The invention also relates to an elongated object comprising a pluralityof the UHMWPE fibers of the invention, wherein said fibers are at leastpartly fused to each other. In one embodiment said elongated object is amonofilament. In a different embodiment, said elongated object is atape. By at least partly fused fibers is herein understood thatindividual fibers are fused at multiple locations along their length anddisconnected between said locations. Preferably, said fibers are fullyfused to each other, i.e. the individual fibers are fused to each otherover essentially their whole length. Preferably, the fusing is carriedout by at least compressing said plurality of UHMWPE fibers under atemperature lower than the melting temperature of the fibers. Themelting temperature of the fibers can be determined by DSC using amethodology as described at pg. 13 of WO 2009/056286. Processes offusing UHMWPE fibers into monofilaments and tapes are known in the artand disclosed for example in WO 2004/033774; WO 2006/040190; and WO2009/056286. It was observed that by using the fibers of the invention,monofilaments and tapes having optimized creep properties were achieved.Such products were suitable for utilisation in applications such asfishing lines; liners; reinforcing elements; antiballistic articles suchas armours; car parts; and architectural applications such as doors.

Hereinafter the figures are explained:

FIG. 1 shows a setup used for the determination of the creep lifetime ofthe UHMWPE fibers of the invention.

FIG. 2 shows a plot of the creep rate [1/s] on a logarithmic scale vs.the elongation in percentage [%] characteristic to an investigated yarn.

The invention will be further explained by the following examples andcomparative experiment, however first the methods used in determiningthe various parameters used hereinabove are presented.

Methods of Measurement:

-   -   IV: the Intrinsic Viscosity for UHMWPE is determined according        to ASTM D1601-99(2004) at 135° C. in decalin, with a dissolution        time of 16 hours, with BHT (Butylated Hydroxy Toluene) as        anti-oxidant in an amount of 2 g/I solution. IV is obtained by        extrapolating the viscosity as measured at different        concentrations to zero concentration.    -   dtex: fibers' titer (dtex) was measured by weighing 100 meters        of fiber. The dtex of the fiber was calculated by dividing the        weight in milligrams to 10;    -   Tensile properties of fibers: tensile strength (or strength) and        tensile modulus (or modulus) and elongation at break are defined        and determined on multifilament yarns as specified in ASTM        D885M, using a nominal gauge length of the fibre of 500 mm, a        crosshead speed of 50%/min and Instron 2714 clamps, of type        “Fibre Grip D5618C”. On the basis of the measured stress-strain        curve the modulus is determined as the gradient between 0.3 and        1% strain. For calculation of the modulus and strength, the        tensile forces measured are divided by the titre, as determined        by weighing 10 metres of fibre; values in GPa are calculated        assuming a density of 0.97 g/cm³.    -   The amount of stabilizer in the fiber was determined by the        well-established FT-IR spectroscopy. A powder sample of the        polymer used to manufacture the fiber therefrom was used to        press a film (typically 600 microns thickness) and its IR        spectrum was recorded. Subsequently, the IR spectrum of films        (having the same thickness as the above) pressed from the above        mentioned powder and also containing known amounts of        stabilizers (typically 0.05 wt %, 0.1 wt % and 0.15 wt %) were        also recorded. The film samples of the above were compared to        determine the peaks given by the presence of the stabilizer.        From these the intensities of the highest peak (at a        representative wavelength) of the stabilizer in the samples        containing thereof were represented versus the concentration of        the stabilizer and the data was linearly fitted to obtain as        so-called calibration line. Normalization can also be carried        out to ensure for a higher accuracy, e.g. in case films having        different thicknesses are analyzed. For this normalization the        most intense peaks adjacent on both sides to the highest peak        (at the representative wavelength) can be used. Subsequently, a        film having the same thickness as the above was pressed from the        polymeric fibers containing the stabilizer in the amount to be        determined. Such film is hereinafter referred to as        fibrous-film. The IR spectrum of the fibrous-films was        determined and the height of the peak given by the stabilizer        recorded at the representative wavelength was compared with the        calibration line. From the calibration line the amount of        stabilizer was determined. Care was taken throughout the        procedure to compress under the same temperature and pressure        conditions films having the same thickness. Alternatively, for        comparing the IR spectrum of films having different thicknesses,        normalization to the peak corresponding to a polymer specific        vibration can be carried out. The skilled person in the art of        FT-IR is aware of such procedure as the peaks corresponding to        polymer specific vibrations can be found in standard FT-IR        textbooks. Typically, this is the peak of the polymer which is        the least sensitive to e.g. crystallization effects and other        different physical properties of the polymer, e.g. molecular        weight, branches, etc. In case combination of stabilizers are        used in the fiber, the above detailed calibration procedure is        applied to obtain calibration lines for each of the specific        stabilizers, and afterwards from the ratios of the peaks at        certain concentration and that of the used concentrations, the        data can be routinely extrapolated to obtain at least the total        amount of the combination of stabilizers in the fiber.    -   As an example of the above, the amount of Chimassorb 944 in a        UHMWPE fiber has been determined as follows: an amount of fibers        was pressed with a pressure of 20 MPa at a temperature of 200°        C.; the amount being chosen to yield a 600 micron thick film. A        transmission spectrum of the film was recorded, followed by        normalization. For normalization the 2018 cm⁻¹ peak was used        (reference; Braco at all, Polymer 46 (2005); 10645-10657); The        peak intensity between 1980 cm⁻¹ and 2100 cm⁻¹ was normalized to        0.5 with a zero point at 1980 cm⁻¹. The peak height at 1530 cm⁻¹        was used for calculation, using the peaks at 1545 cm⁻¹ and 1518        cm⁻¹ as baseline points. The stabilizer concentration was        calculated from the peak height using a calibration line. The        calibration line was calculated from linear regression of the        peak heights at 1530 cm⁻¹ of four pressed UHMWPE powder samples        (same as the one used to manufacture the fiber), which contain 0        wt %; 0.05 wt %; 0.1 wt % and 0.15 wt. % of Chimassorb 944,        respectively. The calibration samples have been prepared by        blending the UHMWPE powder with a solution of the Chimassorb 944        in acetone; whereby the solution to powder ratio was at least        1:10. After evaporation of the acetone, the UHMWPE powders with        different Chimassorb 944 concentrations were consolidated under        a pressure of 20 MPa at a temperature of 200° C. and 600 micron        films were obtained using a microtome.    -   Here also further examples of peaks that can be used to        determine the amount of stabilizers such as e.g. Tinuvin® 765        and 770, may be determined using the peaks at 1728 cm⁻¹ and        using the peaks at 1750 cm⁻¹ and 1710 cm⁻¹ as baseline points        for normalization.    -   Number of alkyl, e.g. ethyl or butyl, branches per thousand        carbon atoms: was determined by FTIR on a 2 mm thick compression        moulded film by quantifying the absorption at 1375 cm⁻¹ using a        calibration curve based on NMR measurements as in e.g. EP 0 269        151 (in particular pg. 4 thereof).    -   Elongational stress (ES in N/mm²) of an UHMWPE, is measured        according to ISO 11542-2A.    -   Creep lifetime (CLT) and elongation during the creep lifetime        were determined in accordance with the methodology described in        the paper “Predicting the Creep Lifetime of HMPE Mooring Rope        Applications” by M. P. Vlasblom and R. L. M. Bosman—Proceedings        of the MTS/IEEE OCEANS 2006 Boston Conference and Exhibition,        held in Boston, Mass. on Sep. 15-21, 2006, Session Ropes and        tension Members (Wed 1:15 PM-3:00 PM). More in particular the        creep lifetime may be determined with a device as schematically        represented in FIG. 1, on untwined yarn samples, i.e. yarn with        substantially parallel filaments, of about 1500 mm length,        having a titer of about 504 dtex and consisting of 900        filaments. In case fibers having a tape-like shape need to be        investigated, fibers having a width of about 2 mm were used. The        yarn samples were slip-free clamped between two clamps (101) and        (102) by winding each of the yarn's ends several times around        the axes of the clamps and then knotting the free ends of the        yarn to the yarn's body. The final length of the yarn between        the clamps (200) was about 180 mm. The clamped yarn sample was        placed in a temperature-controlled chamber (500) at a        temperature of 70° C. by attaching one of the clamps to the        ceiling of the chamber (501) and the other clamp to a        counterweight (300) of 3187 g resulting in a load of 600 MPa on        the yarn. The position of the clamp (101) and that of clamp        (102) can be read on the scale (600) marked off in centimeters        and with subdivisions in mm with the help of the indicators        (1011) and (1021). Special care was taken when placing the yarn        inside said chamber to ensure that the segment of the yarn        between the clamps does not touch any components of the device,        so that the experiment can run fully friction free. An elevator        (400) underneath the counterweight was used to raise the        counterweight to an initial position whereat no slackening of        the yarn occurs and no initial load is applied to the yarn. The        initial position of the counterweight is the position wherein        the length of the yarn (200) equals the distance between (101)        and (102) as measured on (600). The yarn was subsequently        preloaded with the full load of 600 MPa during 10 seconds by        lowering the elevator, after which the load was removed by        raising again the elevator to the initial position. The yarn was        subsequently allowed to relax for a period of 10 times the        preloading time, i.e. 100 seconds. After the preloading        sequence, the full load was applied again. The elongation of the        yarn in time was followed on the scale (600) by reading the        position of the indicator (1021). The time needed for said        indicator to advance 1 mm was recorded for each elongation of 1        mm until the yarn broke.    -   The elongation of the yarn ε_(i), [in mm] at a certain time t is        herein understood the difference between the length of the yarn        between the clamps at that time t, i.e. L(t), and the initial        length (200) of the yarn L₀ between the clamps.    -   Therefore:

ε_(i)(t)[in mm]=L(t)−L ₀

-   -   The elongation of the yarn [in percentages] is:

${{ɛ_{i}(t)}\left\lbrack {{in}\mspace{14mu} \%} \right\rbrack} = {\frac{{L(t)} - L_{0}}{L_{0}} \times 100}$

-   -   The creep rate [in 1/s] is defined as the change in yarn's        length per time step and was determined according to Formula (2)        as:

$\begin{matrix}{{\overset{.}{ɛ}}_{i} = {\frac{ɛ_{i} - ɛ_{i - 1}}{t_{i} - t_{i - 1}} \times \frac{1}{100}}} & (2)\end{matrix}$

-   -   wherein ε_(i) and ε_(i−1) are the elongations [in %] at moment i        and at the previous moment i−1; and t_(i) and t_(i−1) are the        time (in seconds) needed for the yarn to reach the elongations        ε_(i) and ε_(i−1), respectively. The creep rate [1/s] was then        plotted on a logarithmic scale vs. the elongation in percentage        [%] to yield a plot (100) as for example shown in FIG. 2. The        minimum (1) of the plot in FIG. 2 was then determined and the        linear portion (2) thereof after said minimum (1) was fitted        with a straight line (3) which contained also the minimum (1) of        the plot. The elongation (4) where the plot (100) begins to        deviate from the straight line was used to determine the time at        which that elongation occurred. This time was considered as the        creep lifetime for the yarn under investigation. Said elongation        (4) was considered as the elongation during the creep lifetime.    -   Creep properties of Comparative Examples B and C have been        measured at a load of 300 MPa. Such lower load was required to        obtain measurable creep lifetime. The lower load was achieved by        adjusting the weight of the attached counterweight (300) while        considering the titer of the yarns of Comparative Examples B and        C.

Preparation of UHMWPE

UHMWPE a)

A batch of ethyl branched UHMWPE was made according to the preparationdescribed in WO2012139934 under Grade a). The polymerization conditionswere accurately followed, however, only 2.5 ml (0.5 mol/L) of TEOS wasused. THE UHMWPE produced according to this process had an ES of 0.49N/mm² and a level of ethylene branches per 1000C of 0.69. The IV of thepolymer was 20.5 dL/g.

Preparation of UHMWPE Fibers

UHMWPE fibers were produced according to the process described inWO2012139934 with and without the stabilizers. The stabilizers, ifpresent, were solved together with the UHMWPE in the decalin.

The following 3 stabilizers were evaluated: Chimassorb®944(Poly{[[6-[(1,1,3,3-tetramethylbutyl)amino]-s-triazine-2,4-diyl][(2,2,6,6-tetramethyl-4-piperidinyl)imino]hexamethylene[(2,2,6,6-tetramethyl-4-piperidinyl)imino]]}),Tinuvin®765 (Bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate) andTinuvin®770 (Bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate). Thesestabilizers were supplied by BASF.

Pre-Conditioning of UHMWPE Fibers

Potential residues of decalin have been removed by pre-conditioning allthe fibers prior to subjecting the fibers to the creep evaluation. Saidpre-conditioning consisted in subjecting the fibers during 48 hours to atemperature of 100° C. in an air venting oven.

EXAMPLE 1, 2 AND 3

From the prepared UHMWPE a) yarns 1, 2 and 3 were spun each comprising0.6 wt % of stabilizer. The obtained fibers have been pre-conditionedand subjected to a creep performance test at 70° C. under a load of 600MPa. The creep performance data are reported in table 1 below.

COMPARATIVE EXAMPLE A

This example reproduces a yarn according to WO2012139934 by spinningUHMWPE a) without the addition of a stabilizer. The obtained yarn A hasbeen pre-conditioned and subject to a creep performance test. Theproperties of the yarn as well as its creep performance data arereported in table 1 below.

COMPARATIVE EXAMPLE B AND C

have been produced from a UHMWPE sample with an ES of 0.44 N/mm² and0.05 methyl groups/1000C, each a stabilizer free and a stabilized yarnwas produced (Comparative Examples B and C respectively). The obtainedfibers have been pre-conditioned and subjected to a creep performancetest (at 70° C. under a load of 300 MPa). The properties of the yarn aswell as its creep life time (CLT) are reported in table 1 below.

TABLE 1 ES Branching Stabilizer CLT [h] CLT [h] Sample [N/mm²] [/1000 C][wt %] type 600 MPa 300 MPa Example 1 0.49 0.69 (Et) 0.6 Chimassorb ®944 131 Example 2 0.49 0.69 (Et) 0.6 Tinuvin ® 765 111 Example 3 0.490.69 (Et) 0.6 Tinuvin ® 770 98 Comp Exp. A 0.49 0.69 (Et) — 47 Comp Exp.B 0.44  0.05 (Me) — 117 Comp Exp. C 0.44  0.05 (Me) 0.6 Chimassorb ® 944100

1. A creep optimized gel-spun fiber comprising a polyethylene fiber bodyobtained by spinning an UHMWPE comprising alkyl branches (AB) and havingan elongational stress (ES), and a ratio$\left( \frac{A\; {B/1000}\; C}{E\; S} \right)$ of at least 0.2,wherein a stabilizer is present inside the fiber body, characterized inthat the amount of said stabilizer is between 0.05 and 10 parts byweight based on 100 parts by weight of the amount of the PE forming saidfiber body.
 2. The fiber according to claim 1 obtained by spinning anUHMWPE comprising ethyl branches and having an intrinsic viscosity (IV)of at least 5 dl/g, an elongational stress (ES), and a ratio$\left( \frac{C\; 2H\; {5/1000}C}{E\; S} \right)$ of at least0.5, preferably at least 1.0
 3. The fiber according to claim 2 whereinthe UHMWPE has an amount of ethyl branches per thousand carbon atoms(C2H5/1000C) of between 0.60 and 1.10.
 4. The fiber according to claim 1obtained by spinning an UHMWPE comprising butyl branches and having anintrinsic viscosity (IV) of at least 5 dl/g, an elongational stress(ES), and a ratio$\left( \frac{C\; 4H\; {9/1000}C}{E\; S} \right)$ of at least0.2.
 5. The fiber according to claim 1 wherein the IV of the UHMWPE isat least 15 dl/g, preferably at least 19 dl/g.
 6. The fiber according toclaim 1 wherein the UHMWPE has an ES of at most 0.50.
 7. The fiber ofclaim 1 wherein the amount of stabilizer is between 0.1 and 5 parts byweight.
 8. The fiber of claim 1 wherein the stabilizer is a hinderedamine stabilizers (HAS) having a molecular weight of at least 500 g/mol.9. The fiber of claim 1 wherein the stabilizer is a hindered aminestabilizers (HAS) which is soluble in decalin at a level of at least 1g/l at 21° C.
 10. The fiber of claim 1 wherein the stabilizer is chosenfrom the group consisting of phenol stabilizers, organic phosphitestabilizers, organic thioether stabilizers, hindered phenols, aromaticphosphites, amines and combination thereof.
 11. A rope, a crane rope, amooring rope or a cordage comprising the fiber according to claim
 1. 12.A reinforced product containing reinforcing elements wherein thereinforcing elements contain the fiber according to claim
 1. 13.Multi-layered composite articles for ballistic applications e.g. bodyarmor, helmets, hard and flexible shield panels and panels for vehiclearmouring, said articles containing the fiber according to claim
 1. 14.Product containing the fiber according to claim 1, wherein said productis chosen from the group consisting of fishing lines and fishing nets,ground nets, cargo nets and curtains, kite lines, dental floss, tennisracquet strings, canvas, woven and nonwoven cloths, webbings, batteryseparators, capacitors, pressure vessels, hoses, umbilical cables,automotive equipment, power transmission belts, building constructionmaterials, cut and stab resistant and incision resistant articles,protective gloves, composite sports equipment, skis, helmets, kayaks,canoes, bicycles and boat hulls and spars, speaker cones, highperformance electrical insulation, radomes, sails, and geotextiles.